Flat panel display technology is developing rapidly with such devices continuously increasing in size. Exposure using an objective with a large field of view (FoV) can result in an effective increase in yield. However, FoV enlargement for an objective optical system will raise difficulties in design, manufacturing and other aspects. A required large FoV can be alternatively achieved by stitching equally-sized FoVs of several sub-objectives that are arranged in a certain manner. The number of the used sub-objectives is determined by the size of the required FoV. This approach can meet the needs for large FoV, while reducing the optical processing and manufacturing difficulties and providing high compatibility and flexibility.
Due to the stitching of multiple sub-objectives, and because of performance and assembly tolerances of each sub-objective and other factors, imaging positions of the individual sub-objectives may deviate from their theoretical positions. In addition, the large-sized mask may undergo gravity-caused deformations which may lead to deviations in surface profile of the photosensitive substrate. In order to make each imaging FoV be located at its ideal position, each of the sub-objectives is provided with a separate adjustment mechanism for adjusting the position of its imaging FoV to ensure the performance of the whole stitching FoV.
A scanning exposure apparatus equipped with multiple projection optical systems that generate neighboring projection fields stepping forward by predetermined amounts of displacement in the scanning direction, with end portions of neighboring projection fields overlapping each other in a direction orthogonal to the scanning direction, is called a scanning exposure apparatus with multiple lenses (multi-lens scanning exposure apparatus). With such a multi-lens scanning exposure apparatus, the mask is illuminated through multiple slit-shaped illumination regions and is scanned together with the photosensitive substrate simultaneously in a direction orthogonal to the arrangement direction of the illumination regions so that the multiple projection optical systems corresponding to the respective illumination regions expose a pattern on the mask onto the photosensitive substrate.
In an exposure apparatus disclosed in the prior art, focal plane adjustment is accomplished by translating right-angle reflectors disposed in an optical path or a group of wedge plates arranged on the object side, and horizontal shifts of the image are enabled by rotating two parallel plates on the object side respectively about the X- and Y-directions. Additionally, magnification adjustment is made possible by moving any one of three half-lenses on the image side that constitute an afocal optical system, but however, at the same time, introduces a change in the focal plane which has to be offset using the focal adjustment system. In another exposure apparatus, magnification adjustment is accomplished by axial translation of an afocal system consisting of two lenses placed in a catadioptric optical path, and focal plane adjustment is made possible by translation of an afocal system consisting of three lenses disposed on the image side.
As discussed above, in order to ensure good quality of the FoV of stitching objectives, each of the conventional exposure systems employs adjustment mechanisms in the stitching objectives for enabling positional adjustment of the image plane, which increase structural complexity of the objectives and tightness of their internal spaces. In addition, these adjustment mechanisms are driven by respective motor-based actuation systems which require regular repairs and maintenance. Placement of them in the objectives makes them less accessible for such repairs and maintenance operations.